Frequency characteristics of summating potential in Menière's disease.

SP iso-response functions in 9 patients with Menière's disease were examined for differences in the properties between +SP and -SP. The iso-response functions of +SP and -SP exhibited a large difference. The iso-response function for +SP was centered at high frequencies (around 9 kHz in most cases) with fairly steep slopes on both sides towards both higher and lower frequencies, whereas -SP showed a low-pass function. The tendency was found for patients with normal hearing at high frequencies to have a larger Q10dB than patients with a hearing loss. The difference in properties between +SP and -SP suggests the possibility that +SP may provide different information on the pathophysiology of Ménière's disease from that obtained from -SP.

[Effects of urinastatin against nephrotoxicity of cisplatinum].

Nephrotoxicity is the major side effect of cisplatinum (CDDP) and it is often the dose limiting factor. We have studied the effect of urinastatin (US) to decrease the nephrotoxicity of CDDP administration. 28 patients with gynecological cancer treated by chemotherapy including CDDP (13 mg/m2 daily for 5 days) were assigned to two groups, the group with US (n = 14) and the group without US (n = 14). The former was added each 150,000 units of US before and after administration of CDDP. The BUN, serum creatinine (Cre), creatinine clearance (Ccr) and the excretion of beta 2-microglobulin (beta 2-MG) index and N-acetyl-beta-glucosaminidase(NAG)index were measured. The BUN, Cre and Ccr were within normal range during four cycles. However NAG index rose remarkably when CDDP was treated by CDDP. And the increase in NAG index, which reflect the magnitude of renal tubal damage, was less in the group with US than in the group without US. It was suggested that US had effects to reduce nephrotoxicity of CDDP in chemotherapy, and that we could treat patients by high dose CDDP.

Clinical significance of positive summating potential in Menière's disease.

The positive summating potential (+SP) in Menière's disease was compared with that in normal ears and in cochlear deafness of other origin than endolymphatic hydrops in order to assess a specificity of the +SP in Menière's disease. The +SP was recorded in 21 of 47 Menière ears (45%) on stimulation with 8-kHz tone bursts, whereas the +SP was recorded in none of 10 normal-hearing ears and in 1 of 28 ears with cochlear deafness of other origin than endolymphatic hydrops (4%). The incidence of the +SP in Meniére's disease was higher on stimulation with 8-kHz tone bursts than with 4-, 2- and 1-kHz tone bursts and clicks. No correlation between SP amplitudes recorded with 2- and 8-kHz tone bursts was found. The results suggest that Menière's disease may involve a pathophysiological condition which allows the +SP to be frequently recorded.

The relationship of SP and AP findings to hearing level in Menière's disease.

The relationship of summating potential (SP) and action potential (AP) to hearing threshold level was examined in 46 patients with a unilateral Ménière's disease. The SP and AP were recorded with the extratympanic method. The ratio of -SP and AP amplitudes in affected ears to those in contralateral ears (-SP and AP amplitude ratio) at 80 dB nHL of click stimuli was used as parameters of analysis in order to diminish the variability of SP and AP amplitudes among individuals. The results revealed that there is no relationship between -SP amplitude ratio and the hearing threshold level at any frequency, whereas AP amplitude ratio has a significant negative correlation (r = -0.419, p less than 0.01) to the average hearing threshold level at 2-8 kHz, but not at 0.25-1 kHz (p greater than 0.05). The results indicate that an increase in the ratio of -SP amplitude to AP amplitude with the deterioration of the hearing at higher frequencies reported by our previous study (Mori et al., 1987) results from a decrease in AP amplitude rather than an increase in -SP amplitude. The dependence of AP amplitude on hearing threshold level and the independence of -SP amplitude on hearing threshold level suggests that the mechanism underlying the increase in -SP amplitude may be different from that causing the hearing loss in Ménière's disease.

Comparison between AP and SP parameters in trans- and extratympanic electrocochleography.

Results of the comparison of action potential (AP) and summating potential (SP) parameters in trans- (TT) and extratympanic (ET) methods in 2 normal-hearing ears and 20 hearing-impaired ears with various etiologies and audiogram shapes are reported. In normal and impaired ears the TT/ET ratio of N1 amplitude was intensity dependent and was greater at higher intensities than at lower intensities. N1 latency was identical in both methods. The AP waveform was almost identical in both methods in ears except in a noise-induced hearing loss: N1/N2 ratio was greater in the TT method than in the ET method. In the TT method +SP at high frequency tone bursts and -SP at low frequency tone burst were recorded in Menière's disease and progressive sensorineural hearing loss, while in the ET method only -SP was recorded at a tone burst of each frequency. Origins of N1 and N2 and a clinical value of -SP and +SP are discussed.